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Methods to modify the magnetic coercivity and exchange bias field of nanocrystalline antiferromagnetic/ferromagnetic NiO/Ni80Fe20 thin films were investigated for bilayers grown using ion-assisted deposition onto different single crystalline substrates. An enhanced coercivity was found at 298 K for the films deposited on single crystalline MgO (100) and Al2O3 (11-20) substrates. After field cooling the films to 50 K, the NiO/NiFe bilayer grown on Al2O3 (11-20) exhibited the largest exchange bias ( - 25 Oe). The second part of the study investigated ion-beam modification of the ferromagnetic surface prior to the deposition of the NiO layer. A range of ion-beam bombardment energies (VEH) were used to modify in situ the NiFe surface during the deposition of NiO/NiFe/SiO2 films. Cross-sectional transmission electron microscopy showed a systematic reduction in the thickness of the NiFe layers with increasing Ar+ bombardment energies attributed to etching of the surface. In addition, the bombardment procedure modified the magnetic exchange bias of the composite structure in both the as-prepared and field-cooled state.

The amyloid precursor protein (APP) gene family includes APP and the amyloid precursor-like proteins, APLP1 and APLP2. These proteins contain metal binding sites for copper, zinc and iron and are known to have physiological roles in modulating the metal homeostasis in brain cells. Here we report the application of X-ray fluorescence microscopy (XFM) to investigate the subcellular distribution patterns of the metal ions Cu, Zn, Fe, and Ca in individual neurons derived from APP and APLP2 knockout mice brains to further define their role in metal homeostasis. These studies add to the growing body of data that the APP family of proteins are metalloproteins that have shared as well as distinct effects on metals. As we continue to delineate the cellular effects of the APP family of proteins it is important to consider how metals are involved in their actions.

Seven particles captured by the Stardust Interstellar Dust Collector and returned to Earth for laboratory analysis have features consistent with an origin in the contemporary interstellar dust stream. More than 50 spacecraft debris particles were also identified. The interstellar dust candidates are readily distinguished from debris impacts on the basis of elemental composition and/or impact trajectory. The seven candidate interstellar particles are diverse in elemental composition, crystal structure, and size. The presence of crystalline grains and multiple iron-bearing phases, including sulfide, in some particles indicates that individual interstellar particles diverge from any one representative model of interstellar dust inferred from astronomical observations and theory.

The requirements on the spatial and temporal coherence for conventional Coherent Diffractive Imaging (CDI) have been well-established in the literature based on Shannon sampling of the diffracted intensities. The spatial coherence length of the illumination must be larger than twice the lateral dimensions of the sample whilst the temporal coherence length must be larger than the maximum optical path length difference between the two edges of the sample for the highest order diffraction peaks. However, recent approaches to CDI which have included knowledge of the spatial and temporal coherence information in the image reconstruction have allowed us to relax these conventional coherence constraints, extending the applicability of the technique to less coherent sources. In light of these developments it is useful to revisit the idea of a coherence limit in partially coherent CDI and establish a ‘universal’ limit on the partial coherence that can be tolerated without any loss of information. In this paper we present a simple and straightforward description of the limit of spatial and temporal coherence in partially coherent CDI.

Huntington's disease (HD) is a progressive neurodegenerative disorder caused by a polyglutamine-encoding CAG expansion in the huntingtin gene. Iron accumulates in the brains of HD patients and mouse disease models. However, the cellular and subcellular sites of iron accumulation, as well as significance to disease progression are not well understood. We used independent approaches to investigate the location of brain iron accumulation. In R6/2 HD mouse brain, synchotron x-ray fluorescence analysis revealed iron accumulation as discrete puncta in the perinuclear cytoplasm of striatal neurons. Further, perfusion Turnbull's staining for ferrous iron (II) combined with transmission electron microscope ultra-structural analysis revealed increased staining in membrane bound peri-nuclear vesicles in R6/2 HD striatal neurons. Analysis of iron homeostatic proteins in R6/2 HD mice revealed decreased levels of the iron response proteins (IRPs 1 and 2) and accordingly decreased expression of iron uptake transferrin receptor (TfR) and increased levels of neuronal iron export protein ferroportin (FPN). Finally, we show that intra-ventricular delivery of the iron chelator deferoxamine results in an improvement of the motor phenotype in R6/2 HD mice. Our data supports accumulation of redox-active ferrous iron in the endocytic / lysosomal compartment in mouse HD neurons. Expression changes of IRPs, TfR and FPN are consistent with a compensatory response to an increased intra-neuronal labile iron pool leading to increased susceptibility to iron-associated oxidative stress. These findings, together with protection by deferoxamine, support a potentiating role of neuronal iron accumulation in HD.

A phosphorus diffusion gettering model is used to examine the efficacy of a standard gettering process on interstitial and precipitated iron in multicrystalline silicon. The model predicts a large concentration of precipitated iron remaining after standard gettering for most as-grown iron distributions. Although changes in the precipitated iron distribution are predicted to be small, the simulated post-processing interstitial iron concentration is predicted to depend strongly on the as-grown distribution of precipitates, indicating that precipitates must be considered as internal sources of contamination during processing. To inform and validate the model, the iron distributions before and after a standard phosphorus diffusion step are studied in samples from the bottom, middle, and top of an intentionally Fe-contaminated laboratory ingot. A census of iron-silicide precipitates taken by synchrotron-based X-ray fluorescence microscopy confirms the presence of a high density of iron-silicide precipitates both before and after phosphorus diffusion. A comparable precipitated iron distribution was measured in a sister wafer after hydrogenation during a firing step. The similar distributions of precipitated iron seen after each step in the solar cell process confirm that the effect of standard gettering on precipitated iron is strongly limited as predicted by simulation. Good agreement between the experimental and simulated data supports the hypothesis that gettering kinetics is governed by not only the total iron concentration but also by the distribution of precipitated iron. Finally, future directions based on the modeling are suggested for the improvement of effective minority carrier lifetime in multicrystalline silicon solar cells.

Despite its reputation as a poison, arsenic is also a highly effective anti-leukaemia agent. In order to improve on its efficacy, a better understanding of the metabolism of arsenic, including the formation of specific arsenic metabolites, is necessary. In this study XAS was used to gain an understanding of the metabolism of arsenic in human hepatoma cells and microprobe SR-XRF imaging was used to determine potential targets for the identified arsenic species. It was found that the toxic arsenic metabolites, [MMAIII(GS)2] and [DMAIII(GS)], were produced in human cells and that these metabolites potentially interact with DNA or, more probably, proteins associated with DNA transcription.

The evolution during silicon solar cell processing of performance-limiting iron impurities isinvestigated with synchrotron-based x-ray fluorescence microscopy. We find that during industrialphosphorus diffusion, bulk precipitate dissolution is incomplete in wafers with high metal content,specifically ingot border material. Postdiffusion low-temperature annealing is not found to alterappreciably the size or spatial distribution of FeSi2precipitates, although cell efficiency improvesdue to a decrease in iron interstitial concentration. Gettering simulations successfully modelexperiment results and suggest the efficacy of high- and low-temperature processing to reduce bothprecipitated and interstitial iron concentrations, respectively.

Background: Mycobacterium avium subsp hominissuis (previously Mycobacterium avium subsp avium) is an environmental organism associated with opportunistic infections in humans. Mycobacterium hominissuis infects and replicates within mononuclear phagocytes. Previous study characterized an attenuated mutant in which the PPE gene (MAV-2928) homologous to Rv1787 was inactivated. This mutant, in contrast to the wild-type bacterium, was shown both to have impaired the ability to replicate within macrophages and to have prevented phagosome/lysosome fusion. Results: MAV-2928 gene is primarily upregulated upon phagocytosis. The transcriptional profile of macrophages infected with the wild-type bacterium and the mutant were examined using DNA microarray, which showed that the two bacteria interact uniquely with mononuclear phagocytes. Based on the results, it was hypothesized that the phagosome environment and vacuole membrane of the wild-type bacterium might differ from the mutant. Wild-type bacterium phagosomes expressed a number of proteins different from those infected with the mutant. Proteins on the phagosomes were confirmed by fluorescence microscopy and Western blot. The environment in the phagosome of macrophages infected with the mutant differed from the environment of vacuoles with M. hominissuis wild-type in the concentration of zinc, manganese, calcium and potassium. Conclusion: The results suggest that the MAV-2928 gene/operon might participate in the establishment of bacterial intracellular environment in macrophages.

Grating-based x-ray imaging provides three principle kinds of contrast: absorption, phase, and dark-field. Due to the availability of tomographic reconstruction algorithms for the dark-field contrast, it is now possible to take advantage of quantitative scatter information. However, the published algorithm is based on several assumptions that might be violated in reality. We use numerical simulations in order to identify artifacts in the reconstructions, which is crucial for the interpretation of experimental data.